It is well known that when a patient is confined to bed for a prolonged period, he may develop such distressing symptoms as bedsores or rashes on the parts of his body that press on the bed to support his weight. A major cause of the ill effects is the occlusion of the blood capillaries near the surface of the skin caused by the pressure. If a region of flesh is deprived of blood for long, then sores may result.
It is known to provide an inflatable mattress or pad comprising inflatable and deflatable flexible tubes laid side by side across the bed, alternate tubes being joined by conduits, so that the tubes form two interdigitated arrays which are connected to a pump assembly which inflates one array while deflating the other, and which alternates so that each array is periodically inflated and deflated. At any given moment the patient is supported by the tubes of the array which is inflated, whereas the parts of his body which are over the deflated (and therefore collapsed) tubes are subject to substantially no pressure from the mattress, and therefore enjoy a free circulation of blood. Before the constriction of capillaries or other consequence of the pressure on the load-bearing parts of the body can cause harm, the pressure is removed from those parts and re-applied at the formerly pressure-free parts. Thus the mattress ripples, and the weight-supporting areas of the body of the patient are changed.
Plastics materials are generally unpleasant to lie on directly, tending to cause sweating. It is known to interpose between patient and mattress a layer of foam or woollen material, and to make the upper surface of the mattress porous so that air passes through the body support area and in order to dry perspiration.
For ease and cheapness of construction, it is convenient for the tubes to be of plastics material and of substantially circular or elliptical cross-section when inflated. With the prior devices, it is found that if the weight of the patient is very unevenly distributed, for example, when the patient sits up, the tubes bearing the bulk of the weight are insufficiently resilient: the air is forced from the parts of the tubes that are hardest pressed, the patient is effectively supported by whatever is beneath the inflatable mattress, and the benefits of the appliance are not obtained.
This problem might be obviated:
(i) by increasing the pressure of air in the inflated tubes. However, a very considerable increase would be needed to get the desired effect and this would present problems regarding the strength of the material and the pump, and might furthermore result in an unacceptably hard and uncomfortable mattress. PA1 (ii) by increasing the vertical depth of the tubes. However, if tubes of substantially circular cross-section were used, a large diameter would be required, and therefore the patient would be supported in only a few widely-spaced regions, which would not be comfortable. If tubes of greater depth than width were used, the inflated load-bearing tubes would tend to deform and fill the voids left by the deflated tubes, thus removing the desired alternation, unless tubes having internal restraining structure were used. Such tubes are expensive to make.